Abstract
It is known that nitric oxide (NO) may affect myosin heavy chain (MyHC) isoform mRNA transcription in skeletal muscles. The content of NO in soleus muscles decreases during rat hindlimb unloading as well as slow MyHC mRNA transcription. We aimed to detect which signaling pathways are involved in NO-dependent prevention of hindlimb-suspension (HS)-induced changes in MyHCs’ expression pattern. Male Wistar rats were divided into four groups: cage control group (C), hindlimb suspended for 7 days (7HS), hindlimb suspended for 7 days with L-arginine administration (7HS+A) (500 mg/kg body mass), and hindlimb suspended for 7 days with both L-arginine (500 mg/kg) and NO-synthase inhibitor L-NAME administration (50 mg/kg) (7HS+A+N). L-arginine treatment during 7 days of rat HS prevented HS-induced NO content decrease and slow MyHC mRNA transcription decrease and attenuated fast MyHC IIb mRNA transcription increase; it also prevented NFATc1 nuclear content decrease, calsarcin-2 expression increase, and GSK-3β Ser 9 phosphorylation decrease. Moreover, L-arginine administration prevented the HS-induced myh7b and PGC1α mRNAs content decreases and slow-type genes repressor SOX6 mRNA transcription increase. All these slow fiber-type protective effects of L-arginine were blocked in HS+A+N group, indicating that these effects were NO-dependent. Thus, NO decrease prevention during HS restores calcineurin/NFATc1 and myh7b/SOX6 signaling.
Highlights
Skeletal muscles are composed of fibers with different functional properties arranged in a mosaic pattern
In the unloaded group with both L-arginine and L-NAME administration (7HS+A+N), nitric oxide (NO) content was significantly decreased by 46% compared to control
L-NAME blocked all these effects of L-arginine in group 7 days with L-arginine administration (7HS+A)+N, so we can conclude that L-arginine prevents unloading-induced myosin heavy chain (MyHC) I and MyHC IIa mRNAs transcription decreases by affecting the content of NO in soleus muscles of unloaded animals
Summary
Skeletal muscles are composed of fibers with different functional properties arranged in a mosaic pattern. Slow-type fibers are characterized by a high fatigue resistance, a longer duration of contraction, and a lower maximum force. Fast-type fibers demonstrate a high contraction force, but an increased fatigability. The predominance of one of these fiber types in a skeletal muscle determines the phenotype of the muscle. It has been discovered that muscle fiber type is determined by the relative content of slow and fast myosin heavy chain (MyHC) isoforms in the fiber (Schiaffino and Reggiani, 2011).
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